1. Field of the Invention
The present invention relates to a data converter and an image reader using the same data. More specifically, it relates to a data converter which is applied to a facsimile, an image scanner or the like to convert read image data and an image reader using the same data.
2. Description of the Prior Art
In a facsimile, for example, an original image is read pixel by pixel. A reading sensor, such as a one-dimensional CCD (charge coupled device), performs main scanning and subscanning from left to right and from top to bottom along the surface of the original. Thereby the original image is read over the entire surface. In case of recording, a recording head such as a thermal head performs similar scanning with respect to recording paper. Such a scanning method is set by the so-called G3 standard in the facsimile.
A facsimile of the so-called serial system has come into use in recent years. In such a facsimile of the serial system, a reading sensor having a plurality of pixels along the subscanning direction in the G3 standard mechanically moves along the main scanning direction. After such a single movement, the reading sensor is moved in the subscanning direction in a distance corresponding to the number of pixels thereof, for reading an original image. Furthermore, in the facsimile of the serial system, a recording head also has a plurality of pixels along the subscanning direction in the G3 standard similar to the reading sensor, and performs the recording by scanning recording paper in a similar manner to the reading sensor,
The aforementioned facsimile of the serial system has been widely used in recent years, since the pixel numbers of the reading sensor and the recording head can be decreased to reduce the cost. For example, although a device having 2048 pixels is required for a reading sensor or a recording head which electrically performs the main scanning along the G3 standard, such a device may have only 64 to 128 pixels in the serial system.
In a facsimile, a transmitted image cannot be reproduced in a receiving area unless the order of transmission of image information is unified. The aforementioned G3 standard is adapted to unify such order.
In the facsimile of the serial system, conversion is required in order to transpose the order of image data for transmission/receiving since the scanning method thereof is absolutely different from that along the G3 standard. Such a conversion of the image data is performed in so-called hardware manner by various types of arithmetic circuits or in a so-called software manner by a CPU (central processing unit).
In the aforementioned method of converting image data in the hardware manner, complicated circuit structure having an extremely large scale is required in order to cope with the main scanning length and the pixel number of the facsimile in a counterpart as well as coping with a variation in the main scanning length. On the other hand, in the method of converting image data in the software manner, the processing speed of the CPU becomes a factor since pixel-by-pixel processing, i.e., bitwise processing, cannot be performed at a high speed although processing in units of eight or 16 bits may be quickly performed. When the CPU is implemented by a Z80 to receive basic clocks at a frequency of 6 MHz, for example, about 25 msec. is required for each scanning line. This is the time limit in consideration for image processing operations such as compression or expansion.